1. Field of the Invention
The present invention relates to a circuit breaker, and more particularly to an arc chute assembly for a circuit breaker which facilitates an assembly between grids and sidewalls.
2. Description of the Background Art
As shown in FIG. 1, a general circuit breaker includes a case 10 formed of an insulation resin material. Inside the case 10 there are provided a trip apparatus and a switching apparatus therein.
The trip apparatus includes a bimetal 20 and a heater 40 disposed below the bimetal 20 and having a fixing core 30 attached thereto. The heater 40 is connected to a load terminal base 50.
The case 10 also includes an amateur 60 disposed at a side portion of the bimetal 20 and having a protrusion (not shown) on each side of the central portion thereof, thereby being operated back and forth while being fixed to a wall of the case 10.
At this time, the bimetal 20 and the amateur 60 are respectively formed of a plurality of pairs thereof. A protrusion (not shown) formed on upper portions of the bimetal 20 and the amateur 60 is provided adjacent to a strip cross bar 70 formed across a side thereof.
At a side portion of the trip cross bar 70 there is formed a protrusion (not shown) with regard to the bimetal 20 and the amateur 60, that is, a protrusion 70a which corresponds to respective poles, and at another side portion of the trip cross bar 70 there is formed a protrusion which is to push a latch holder 80.
Also, the switching apparatus is formed of a mechanical unit operated in accordance with the trip apparatus, and of a stable contact 90 and a movable contact 100.
The stable contact 90 is attached to an upper portion of the stable contact point 120 coupled to the source terminal base 110, and the movable contact 100 is attached to a lower surface of the movable contact point 130.
Also, a holder 140 a side portion of which is connected to the movable contact point 130 is coupled to a shaft 150 formed along an elongated axis.
At this time, the movable contact point 150 is movable upwardly and downwardly having as its center a stable shaft 170 connected to a side plate 160. An arc extinguishing chamber formed of grids 180, arc runner grids (not shown) and side walls (not shown) is provided outside an operational space of the movable contact point 150. Here, an arc becomes extinct in the arc extinguishing chamber.
The mechanical unit is formed of a pair of bimetal 20 and amateur 60 disposed at a central pole thereof, and it also includes a latch 190 moving upwardly and downwardly on the axis of the latch pin 160a fixed to the side plate 160, and a latch holder 80 a side portion of which is hooked on the latch 190 and another side portion of which is coupled to the trip cross bar 70.
At a side portion of the holder 140 there is provided a toggle link 200 connected by use of the holder pin 140a. An upper link 220 is connected to the link pin 210 at an upper portion of the toggle link 200 by a side portion thereof, and coupled to the latch 190 using the upper link pin 220a by another side portion thereof.
Here, the link pin 210 is hooked on the spring 240 attached to the lever 230, and a manual manipulation handle 250 is attached to the lever 230.
The thusly constituted general circuit breaker is a mechanical device for protecting an overflow of current onto a low pressure internal electrical path, and it is reusable after a circuit breaking operation thereof with regard to a switching function of load current and breakdown current.
The current flow steps in a normal condition of the circuit breaker follow the steps of: current terminal base 100.fwdarw.stable contact point 120.fwdarw.stable contact 90.fwdarw.movable contact 100.fwdarw.movable contact point 130.fwdarw.heater 30.fwdarw.load terminal base 50.
However, when there occurs a charge current such as an overcurrent which exceeds a rated current at the circuit breaker, or a short current, the operation of the circuit breaker is as follows.
When there flows an overcurrent that exceeds a rated current through the circuit breaker, the bimetal 20 becomes crooked so that the bimetal 20 carries out a trip operation as a delay trip operation in which the trip cross bar 70 is pushed in a slow mode, and when there occurs a charge current such as a short current, there occurs a strong magnetic field at the fixing core 30. Due to the strong magnetic field, a lower portion of the amateur 60 becomes instantly sucked and at the same time the protrusion (not shown) formed at an upper portion of the amateur 60 comes to press the trip cross 70 as an instant trip operation in which the trip operation is instantly executed.
By use of such a delay trip operation of the bimetal 20 or such an instant trip operation of the amateur 60, when the bimetal 60 or the amateur 60 presses the trip cross bar 70, the trip cross bar 70 becomes rotated, and accordingly when the latch holder 80 is pushed, the latch 190 hooked on the latch holder 80 is released and at the same time the upper link 220 and the toggle link 200 are bent in accordance with the tension of the spring 240 which pulls the link pin 210.
As the upper link 220 and the toggle link 200 are bent, the holder 140 connected to the toggle link 200 by the holder pin 140a and the movable contact point 130 abruptly springs up, thereby opening the stable contact 90 and the movable contact 100.
The holder 140 and the movable contact point 130 are connected in common to the shaft 150 which is connected to the respective poles, so that in accordance with the pole-opening of the stable contact 90 and the movable contact 100 with regard to the central pole the shaft 150 allows other contacts with regard to the respective poles to simultaneously be opened.
At this time, the stable contact 90 and the movable contact 100 are pole-opened and at the same tim there occurs an arc discharge between the stable contact 90 and the movable contact 100.
The thusly generated arc discharge stays for a short while in the stable contact 90 and then the arc discharge moves to the arc extinguishing chamber in accordance with a sudden upward bouncing of the movable contact point 130 as a sudden disconnection.
Then, as the movable contact point 130 moves to an upward direction, the stable contact point 120 becomes further distanced from the movable contact point 130, and accordingly the arc moves toward an internal portion of the grids 180 by an electromagnetic force generated between the grids 180 in the arc extinguishing room and the arc current.
The arc that has moved inside the grids 180 are serially partitioned according to the grids aligned on every other floor therein, and the arc resistance becomes rapidly increased and accordingly the arc voltage becomes rapidly increased by related factors, such as a cathode effect of the grids 180 in which when the arc comes into the arc extinguishing chamber, the grids 180 are respectively turned to positive poles or negative poles, a cooling effect in which the arc is partitioned into shorter arcs between the grids 180 and extinguished in the air by cooling, and a pressure effect according to an arc energy by an increased magnetic flux density with regard to a pressure increase in the arc extinguishing chamber.
When the arc voltage surpasses the source voltage, it becomes difficult for the arc voltage to maintain the arc voltage so that the arc is extinguished. Accordingly, there occurs a voltage corresponding to the source voltage between the stable contact 90 and the movable contact 100, thereby carrying out the circuit breaking operation.
The conventional arc chute assembly for extinguishing the arc will now be described with reference to FIGS. 2 and 3.
The conventional arc chute assembly includes a plurality of grids 180 formed of U-shaped metallic plates for inducing magnetism, and a plurality of side walls 280 formed of insulation material.
The grids 180 respectively include a plurality of engagement protrusions 180a extended from each side thereof and cut off by the respective centers thereof. The side walls 280 includes a plurality of slots 280a for receiving corresponding ones of the engagement protrusions 180a.
The combining steps between the grids 180 and the side walls 280 for forming the arc extinguishing chamber will now be described.
The grids 180 including the engagement protrusions 180a are fixed using a gig and then the grids 180 are respectively inserted into a corresponding one of the engagement slots 280a formed in the side walls 280. In order for the grids 180 not to escape from the side walls 280, the side walls 280 are bound by a rubber string.
The respective cut-off portions of the engagement protrusions 180a are opened to each side thereof by employing a rivetting process, thereby fixing the grids 180 to the side walls 280.
Likewise, the plurality of grids 180 are stacked with a space therebetween between the side walls 280, and the assembled arc chute assembly is mounted in the arc extinguishing chamber provided in the circuit breaker.
However, the conventional arc chute assembly allows the grids 180 to be inserted into the side walls 280, and in order for the grids 180 not to be released from the side walls the side walls 280 are fixed by use of a rubber string and there is further followed a rivetting process for the fixture, thereby disadvantageously increasing processing steps as well as requiring an increased working time.